This invention relates to medical devices, especially to stent carrying balloon catheters, for use in angioplasty and other procedures of vessel repair. Angioplasty is an efficient and successful method of opening stenoses in the vascular system.
In a popular form of angioplasty, a balloon catheter is advanced through the vascular system until the balloon, which is carried at the distal end of a catheter shaft, and which may carry an expandable stent, is positioned across the stenosis or damaged vessel. This movement through the vessels prior to and during positioning is a first critical step in this form of angioplasty. During movement the stent may—especially if the catheter is lubricated—slip from the balloon. To counter this, there is a constant need for improved “stent retention”. By then inflating the balloon, pressure is applied to the obstruction which is moved by pressing it against the inner wall of the vessel, whereby the vessel is opened for improved flow. Due to the expansion of the balloon, the stent, which—if used—is situated on the balloon, is also expanded for aiding in repairing the vessel wall and hindering obstruction. This moment of opening-up of the folded balloon is a second critical step in this form of angioplasty. As the stent is mounted on the central, cylindrical portion of the balloon, the cones of the balloon open first when the balloon is inflated. In case the proximal balloon cone opens before the distal balloon cone there is a risk that the stent can slip off the balloon and get lost in vasculature. In case the balloon cones open symmetrically as intended and in case the frictional forces between the balloon and the stent are low, as is the case especially with smooth material like Nylon forming the balloon, there is a risk that the stent will be compressed longitudinally between the opening balloon cones thus foreshortening of the stent. Is increased. It is therefore another important need to counter this complication which is hindering a correct positioning of the stent. As a last step the stent is then released by deflating the balloon reducing its circumference until refolding of the balloon occurs followed by removal of the balloon and catheter from the vessel. In some cases the refolding is insufficient leading to deformations, like, e.g., the so called “pancake-effect”, in which the refolded balloon does not reach the optimal minimum—mostly circular—size.
There are various types of balloon catheters. One type is fed over a guide wire (i.e., “over-the-wire” catheters) and another type serves as its own guide wire (“fixed-wire” catheters). There have been development variations of these two basic types: the so called “rapid exchange” type catheter, “innerless” catheters, and others. The term “balloon catheter” as defined in this invention is meant to include all the various types of angioplasty catheters which carry a balloon for performing angioplasty and any other type of stent carrying balloon catheter. Balloon catheters also have a wide variety of inner structure, such as different lumen design, of which there are at least three basic types: triple lumen, dual lumen and co-axial lumen. All these varieties of internal structure and design variations are included in the definition “balloon catheter” herein.
If a balloon catheter is used in percutaneous transluminal coronary angioplasty (PTCA), it is typically advanced through a guide catheter to a preselected vessel location, such as the aorta, for example. Using fluoroscopy, the surgeon advances the catheter until the balloon is located across the stenosis or obstruction. This may involve the use of a guide wire over which the catheter is moved or alternatively the catheter may act as its own guide wire.
The use of stents, balloons, catheters, especially balloon catheters and other medical devices etc. in minimal invasive surgery, especially in the cardiovascular field, has—over the last years—shown a high growth. As a consequence the need for modifications to the materials used fulfilling the highly specialized needs in the field of different medicinal devices has clearly risen. Especially in the field of vascular used balloons there was a clear desire for a modified material showing a suitable compliance, a high burst pressure, but also a good and dependable “stent retention” as well as reduction of “foreshortening” of the stent upon delivery.
U.S. Pat. No. 6,635,078 B1 provides a solution in which either to the inside of the stent or to the outer surface of the balloon an adhesive is applied in defined areas. Besides the first disadvantage of a further production step the adhesive usually has to be chosen well in regards to its adhesion strength to avoid further complications through hindrance of a release of the stent from the balloon after expansion or a further resistance during expansion of the balloon due to the further adhesive binding with the risk of an abrupt opening.
U.S. Pat. No. 6,306,144 B1 provides a solution in which in a certain pattern a single layer balloon catheter is lubricated in certain areas and in other areas not or less lubricated or treated with an adhesive. Besides the first disadvantage of having to adhere to very defined patterns during production either the adhesive used has to be chosen well as to avoid further complications through hindrance of release or abrupt opening. On the other hand, due to the very nature of a fluid lubricant neighboring lubricious material can easily flow into the less- or non-treated areas, even worsening the foreshortening and other slipping of the stent.
The present invention is aimed at having an improved grip or adhesion force, i.e., high friction forces between the surface of the balloon and the stent (or graft etc.) to help in better stent retention and especially avoiding the longitudinal slip of the stent during expansion of the balloon thus avoiding longitudinally compression of the stent by the increasing balloon cones and thus minimizing foreshortening of the stent during expansion, but without using an adhesive on the outer surface of the balloon nor on the inner surface of the stent. This invention thus avoids the sub-optimal behavior of the known balloons during movement in the vessel and during expansion at the same time avoiding the problems associated with prior solutions.